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(p200300cbc704100021d5831de107fbd6.dip0.t-ipconnect.de. [2003:cb:c704:1000:21d5:831d:e107:fbd6]) by smtp.gmail.com with ESMTPSA id bp28-20020a5d5a9c000000b00273cd321a1bsm25937199wrb.107.2023.01.16.02.17.53 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 16 Jan 2023 02:17:54 -0800 (PST) Message-ID: <06423461-c543-56fe-cc63-cabda6871104@redhat.com> Date: Mon, 16 Jan 2023 11:17:52 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.6.0 Subject: Re: [PATCH 21/46] hugetlb: use struct hugetlb_pte for walk_hugetlb_range To: Peter Xu , James Houghton Cc: Mike Kravetz , Muchun Song , David Rientjes , Axel Rasmussen , Mina Almasry , Zach O'Keefe , Manish Mishra , Naoya Horiguchi , "Dr . David Alan Gilbert" , "Matthew Wilcox (Oracle)" , Vlastimil Babka , Baolin Wang , Miaohe Lin , Yang Shi , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20230105101844.1893104-1-jthoughton@google.com> <20230105101844.1893104-22-jthoughton@google.com> Content-Language: en-US From: David Hildenbrand Organization: Red Hat In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12.01.23 22:33, Peter Xu wrote: > On Thu, Jan 12, 2023 at 04:17:52PM -0500, James Houghton wrote: >> I'll look into it, but doing it this way will use _mapcount, so we >> won't be able to use the vmemmap optimization. I think even if we do >> use Hugh's approach, refcount is still being kept on the head page, so >> there's still an overflow risk there (but maybe I am >> misunderstanding). > > Could you remind me what's the issue if using refcount on the small pages > rather than the head (assuming vmemmap still can be disabled)? The THP-way of doing things is refcounting on the head page. All folios use a single refcount on the head. There has to be a pretty good reason to do it differently. -- Thanks, David / dhildenb